Ok, with the 302 Closed chamber heads, you get about 11:1 Compression (ball opark figure)3" stroke. put the same heads on a 351 Cleveland, get the extra .5" to get a total of 3.5 of stroke and the Compression remains RELATIVELY 11:1. Well, what is to stop us from going to an extra .5" of stroke? I guess I am bringing up the 400 Question again. I am just trying to learn more.

Ok, with the 302 Closed chamber heads, you get about 11:1 Compression (ball opark figure)3" stroke. put the same heads on a 351 Cleveland, get the extra .5" to get a total of 3.5 of stroke and the Compression remains RELATIVELY 11:1. Well, what is to stop us from going to an extra .5" of stroke? I guess I am bringing up the 400 Question again. I am just trying to learn more.

Jeff ... Compression on a 302 ci engine with these heads would not be 11:1 ... much smaller cylinder volume than our 351C. I reckon they deliver maybe 9.5:1 ... and I'm guessing, I'm sure someone in the forum knows exactly.

What is happening in this post is taking heads with a slightly smaller combustion chamber than the "normal" 351C quench heads and sticking them on top of our bigger cube engine. Net compression ratio difference is minimal on our engines.

When you take the quench head and stick on a 400 ... You would expect the compression to jump big time ... But, it doesn't because the deck clearance is huge on the 400 which keeps compression down ...

I have a US 351C. I am going to put on Aussie heads and a pretty aggressive cam that requires 10:1 - 11:1 compression. I imagine I won't be under 10 by putting on the 302 2V Aussie Cleveland heads. But I was looking to see what compression I could expect only with the addition of the smaller cc 302 Aussie Heads on my stock US 351C.

From what I read though I think somewhere around 10.5 - 11.

My other question is what is the stock compression ratio on a stock 70 351C 4V engine. The manual says 11:1 which seems a little high. So I was thinking with the addition of smaller chamber heads the compression might be higher than desired. Around 12:1 or higher, but, again from the posts, I think it won't come out that high.

So what piston do we assume here? When looking at Speed Pro (formerly TRW) pistons, I see 10.7ish:1. You calculate 11.3:1 on Keith Black pistons.

What can we assume about the pistons? Different heights? Keith Blacks give back 2cc, and the Speed Pros say they give back 1.5cc. I really would have expected that Speed Pros would have advertised a higher compression if their valve reliefs ahve less cc's.

Larry, how are you gonna account for that much compression? I know you are (were) running 11.1:1 on the Beast... are you gonna be able to squeeze in 11.3:1 on pump gas?

speedar - something looney about your numers... your head gasket is .047" with 4.62 cc, and your deck is .048" with 10.17cc Those heights are nearly identical, the cc's should be too... unless there is something goofy about the head gasket that I am not considering.

The "engine guru" (in the circles I run in)
has indicated to me that the extra bit of compression (11.25 vs 11.1) won't be a problem with the Aussie quench heads.

Understand though, I haven't done this, so I can't speak from personal experience.

I am building an Aussie 2V motor, but will be running an existing rotating assembly including pistons that have a slight dish so I figure (best estimate) I'll be running 10.3 or something like that in my Aussie.

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